1. Field of the Invention
The present invention relates to the plating of aluminum and aluminum alloys, and, more particularly, to the plating of 390 aluminum alloys with iron. 2. Description of Related Art
In the use of aluminum internal combustion engines with aluminum pistons for vehicles, it is essential that either the piston or the cylinder bore be coated with another metal harder than aluminum to prevent piston skirt scuffing during cold starts. Commonly, an iron coating is plated onto the surface of the aluminum pistons, generally employing a copper undercoat.
In one process, copper cyanide and iron chloride baths are used in the plating. Copper cyanide is a highly toxic and tightly regulated material. The iron chloride bath is also a highly toxic and extremely corrosive bath that is very destructive to the equipment around it.
An alternative approach is to insert an iron sleeve into the cylinder bore. Still another approach is to coat the inside of the bore with a suitable metal alloy by thermal spray coating processes and then re-machining the bore. These approaches are estimated to be 8 to 14 times as expensive as piston plating.
It is desired to provide a method, preferably inexpensive, for plating aluminum pistons with an acceptable iron coating that will pass all the required adhesion, hardness, and abrasion tests without using highly toxic or hazardous substances.